In the past, it has been extremely difficult and expensive to replace the metal seal rings of high pressure steam valves such as those found in power plants and on naval vessels. Typically, valves of this type come in a range of sizes (1 - 12 inches) and must be extremely heavy in order to function properly in systems where the steam pressure may range from 600 to 1500 psi. Because the valves are welded in the steam lines in which they are used, it is extremely difficult and very expensive to remove the valves from the system for transporting them to a shop for repair. Typically, it has in the past cost several thousand dollars to repair, transport and reinstall one small valve, and upwards of ten thousand dollars to repair one valve over the six inch size. On the other hand, it is also difficult and, more often than not, impossible to repair the valves without removing them from the system. This is due in part to the fact that the valves are often located in small spaces impeded by piping and other valves so that it is impossible to reach them with the bulky tools presently available for refinishing the valve seal ring seats. It is also due to the fact that the prior art tools were extremely heavy. This is particularly true where the valve, though accessible, is located near a bulkhead or near a compartment ceiling on a naval vessel. A typical prior art tool for refinishing the seal ring seats of such valves has weighed approximately 900 to 1,000 pounds and has required the services of three men for several hours in order to set it up in proper alignment for the refinishing of one valve seal ring seat.
Recently, a portable boring bar was developed which solved many problems of the prior art. This portable boring bar is disclosed in U.S. Pat. No. 3,881,396, which is assigned to the present inventor. While the portable boring bar disclosed in the aforementioned patent solved many of the problems of the prior art, it has not proved to be entirely satisfactory in operation because of a tendency to "chatter" and bore "out-of-round". It has been found that these problems result from a lack of strength of the main housing support, and the fact that the design permits dirt and other foreign particles to enter the tool and wear surfaces which must be maintained within close tolerances.